This invention relates to optically coupled relays and more particularly to optically coupled relay circuits which employ adjustable means to insure accurate operation.
The utilization of optical coupling of switching circuits is a well-known method of isolating a control signal from the controlled circuit. Numerous problems have been encountered with such known optically coupled circuitry, including, but not limited to; variations in individual photosensitive circuit sensitivity to common mode noise, inconsistent response to variations in load conditions, dv/dt breakdown and the problems encountered due to switching during high voltage periods of the line voltage.
One example of a known optically coupled relay circuit which utilizes a solid state bilateral switching device and a photodarlington may be seen on page 21 of "Photon Couplers," General Electric, Semiconductor Products Department, Auburn, N.Y., No. 200.62. The circuit depicted therein makes no attempt to adjust the sensitivity of the photosensitive transistor or to compensate for variations in loads, but merely controls a triac through a diode bridge.
A more sophisticated example of such circuitry may be seen in a Hewlett Packard publication, "Electrical Isolation Using the HP 5082-4310,+ No. 909, 1968. The circuit depicted therein utilizes a preamp with a high frequency response to increase the high speed performance of the coupler. Again, there is no method disclosed of assuring uniform sensitivity or compensation due to load variations.